Light guide plates are devices to convert a point light source/line light source into a plane light source, and widely used in backlight modules of LCD displays. A light guide plate typically employs optical grade acryl (PMMA) or optical PC (polycarbonate) as a base material, may be of various shapes including a circular shape, a elliptical shape, an arc shape and a triangle shape, and have advantages such as ultra-thin profile, ultra-brightness, homogeneous light guiding and energy saving.
In conventional electronic devices comprising LCD displays, typically a light guide plate of the planar structure as shown in FIG. 1 is used, with a light source 12 provided on one side thereof. As the electronic devices comprising LCD displays become lighter and thinner continuously, the shape of the light entry side of the light guide plate is also becoming more irregular. A profiled light guide plate 21 is shown in FIG. 2, different from the planar light guide plate 11 in that: the profiled light guide plate 21 comprises a ramp X towards the position of the light source 22 (i.e., the light entry side), and the light guide plate extending from one side of the ramp X is tapered; however, there occur at least problems as described later during application of the profiled light guide plate.
An optical path of the light beam in the profiled light guide plate 31 with the ramp X is shown in FIG. 3. Under the illumination of the light source 32, the light beam R31 that would have been capable of being fully reflected in the planar light guide plate (the reflected light beam R32 represented by the dash line is the reflected light beam in case of being fully reflected in the planar light guide plate shown by the dash line) may not be fully reflected due to the ramp X, and is refracted at the ramp X, forming a refracted light beam R33 represented by the solid line. This leads to a large amount of light leakage from the ramp X, forming bright lines at such ramp X. The picture quality of the LCD display comprising such profiled light guide plate is since worsened, failing to meet the needs of the consumers.